PostGIS & Spatial SQL

Purpose: correct-and-fast spatial SQL. The two recurring failure modes are semantic (geometry vs geography, SRID mismatches → wrong answers) and performance (missing index usage → hour-long joins); this skill guards both.

When the database is the right tool

Move from files/GeoPandas to PostGIS when any of: features > a few million, concurrent readers/writers, repeated ad-hoc querying, a serving API on top, or transactional integrity needs. For single-shot analytical scans over GeoParquet, DuckDB Spatial is often the fastest zero-install path — same SQL mindset, no server.